Handle serialized binary data in encrypted columns

Calling `serialize` is not always possible, because the column type
might not expect to be serializing a String, for example when declared
as serialzed or store attribute.

With binary data the encryptor was passed an
`ActiveModel::Type::Binary::Data`` and returned a `String``. In order to
remain transparent we need to turn the data back into a
`ActiveModel::Type::Binary::Data` before passing it on.

We'll also rename `serialize`` to `text_to_database_type` to be a bit
more descriptive.

activerecord/lib/active_record/encryption/encrypted_attribute_type.rb

@@ -100,7 +100,7 @@ def decrypt_as_text(value)
         end
 
         def decrypt(value)
-          reserialize decrypt_as_text(value)
+          text_to_database_type decrypt_as_text(value)
         end
 
         def try_to_deserialize_with_previous_encrypted_types(value)
@@ -140,7 +140,7 @@ def encrypt_as_text(value)
         end
 
         def encrypt(value)
-          reserialize encrypt_as_text(value)
+          text_to_database_type encrypt_as_text(value)
         end
 
         def encryptor
@@ -159,9 +159,9 @@ def clean_text_scheme
           @clean_text_scheme ||= ActiveRecord::Encryption::Scheme.new(downcase: downcase?, encryptor: ActiveRecord::Encryption::NullEncryptor.new)
         end
 
-        def reserialize(value)
-          if cast_type.binary?
-            cast_type.serialize(value)
+        def text_to_database_type(value)
+          if value && cast_type.binary?
+            ActiveModel::Type::Binary::Data.new(value)
           else
             value
           end

activerecord/test/cases/encryption/encryptable_record_test.rb

@@ -397,6 +397,8 @@ def name
   test "binary data can be encrypted" do
     all_bytes = (0..255).map(&:chr).join
     assert_equal all_bytes, EncryptedBookWithBinary.create!(logo: all_bytes).logo
+    assert_nil EncryptedBookWithBinary.create!(logo: nil).logo
+    assert_equal "", EncryptedBookWithBinary.create!(logo: "").logo
   end
 
   test "binary data can be encrypted uncompressed" do
@@ -406,6 +408,11 @@ def name
     assert_equal high_bytes, EncryptedBookWithBinary.create!(logo: high_bytes).logo
   end
 
+  test "serialized binary data can be encrypted" do
+    json_bytes = (32..127).map(&:chr)
+    assert_equal json_bytes, EncryptedBookWithSerializedBinary.create!(logo: json_bytes).logo
+  end
+
   private
     def build_derived_key_provider_with(hash_digest_class)
       ActiveRecord::Encryption.with_encryption_context(key_generator: ActiveRecord::Encryption::KeyGenerator.new(hash_digest_class: hash_digest_class)) do

activerecord/test/models/book_encrypted.rb

@@ -49,3 +49,10 @@ class EncryptedBookWithBinary < ActiveRecord::Base
 
   encrypts :logo
 end
+
+class EncryptedBookWithSerializedBinary < ActiveRecord::Base
+  self.table_name = "encrypted_books"
+
+  serialize :logo, coder: JSON
+  encrypts :logo
+end